The texture of the pattern explains a good deal of it. There will almost always be a decline in finish quality of the casting. Sometimes its hardly noticable with an excellent sand (which you probably have) and good technique, so if you want a very smooth casting you must start with a very smooth pattern. It's not uncommon for oil sands to actually reproduce fingerprints on your casting. Pete
Wow! I am seriously under-estimating the level of detail that can be captured by oil sand in that case. Certainly food for thought and thank you for highlighting this.
See JEFF! Quit playing in kitty litter and step up your game! When you're light on spare time, ya gotta make every minute count!
I'm thinking you should recast them and change up the ingate a little bit to correct the issue. Gate into the back side of the pattern, the part would be in the cope and the gating in the drag. With the gating only as thick at the pattern about 1/4" long just before it enters the part...
Yeah, cheers @DavidF. After cleaning up one of them, I have realised it's going to be extremely difficult to polish the engraving surface into the corners where the border is - I just don't have the means to do this well. After speaking to my "customer" he agreed that a simple flat plaque would be perfectly alright. So I may well re-cast them as simple flat pieces. But I will certainly take on board your suggestion above.
So I thought I'd try a re-cast but this time I used simple flat patterns with no border (thinking this would make clean-up more straight-forward). So here's the mould complete before pattern removal ... So exactly as before, but this time the cast wasn't a complete success. I think I was unlucky this time and ended up trapping air in those two failed moulds. Perhaps some additional venting would ensure more success? I'd be interested to hear folks opinions on this. Also, given that the patterns were very smooth plastic, I was somewhat disappointed with the quality of the cast. As you can see it's got a very course finish ... I would have expected a smoother finish than this. I can only assume this has something to do with the way I'm packing the sand but again, I'd be keen to hear any thoughts you guys and gals may have. Many thanks in advance.
So, I am pretty much finished with these as they stand ... They have been sanded and polished solely by hand. Besides my dremel (which, as it happens, I haven't used on these) I have no power tools to assist with this process. I think to improve upon this finish will require a significant amount of additional time ... which ain't happening! I may give the dremel a go to see if I can improve things some more with that.
They look good from where im sitting.... A dremel tool works for polishing but like you said, its going to take time. If you plan on making more shiny stuff you might want to get yourself a decent buffer. Even the ones from Harbor freight will make quick work of things..
Cheers David. When you say "buffer" are you referring to those bench mounted, spinney things?! Along these lines ... https://www.amazon.co.uk/Bench-Grinder-Polisher-Polishing-Machine/dp/B0796196LF?ref_=fsclp_pl_dp_3 ??
70pound? JUMP on that thing NOW. I've got way more in my buffer I had to cobble together from a motor, pillow blocks and a rod. Your pieces came out really nice.
I recently picked up one of these and swapped out the grinding wheel for a buffing wheel. https://www.princessauto.com/en/detail/combination-2-in-belt-sander-and-6-in-grinder/A-p8532285e So far, so good. Jeff
Look at this embarrassing polisher I set up years ago. With that said, it has the balls to do some fine aluminum manifold polishing. Ya just gotta keep fingers away from the belt! Someday I'll rebuild it.
Thanks Jason. Loving your Heath-Robinson buffer! That looks fantastic. That sanding belt would have been perfect for my plaques.
There's nothing wrong with your setup Jason, there used to be a dedicated cast spindle housing for a shaft and two ball bearings for just that purpose. My two castings that I've been churning out are for spindles for wire wheels, conditioning wheels and diamond wheels. I also have a 2" x 3Hp belt grinder with pillow blocks.